Engineering testing, monitoring and characterization

Authored by: Paul S. Addison

The Illustrated Wavelet Transform Handbook

Print publication date:  July  2002
Online publication date:  July  2002

Print ISBN: 9780750306928
eBook ISBN: 9781420033397
Adobe ISBN:


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Wavelet analysis has been applied to a variety of pertinent problems in engineering. In this chapter, we review a selection of these, including the assessment of machine processes behaviour; condition monitoring of rotating machinery; the analysis of nonlinear and transient oscillations; the characterization of structural impacting; the interrogation of NDT signals; and the characterization of rough surfaces. As with the fluid problems described in the previous chapter, the choice of the most appropriate wavelet to use in the analysis of engineering problems depends very much on the nature of the data itself. Both discrete and continuous (usually complex) wavelets have been used to monitor rotating machinery such as gears, shafts and bearings. Discrete wavelets are favoured when, for example, a small number of data are required as input to a classifier such as a neural network. Continuous wavelets are favoured when high temporal resolution is required at all scales. Complex continuous wavelets are well suited to the free vibrations of plates and beams. The temporal records of such vibrations quickly exhibit a high degree of complexity due to the superposition of multiple wavegroups (from multiple reflections at the specimen edges) whose group velocity is frequency dependent. Complex continuous wavelets are able to unfold these signals in time and frequency, allowing for the decoupling of vibration modes. Most surface characterization work has used discrete wavelets, whose coefficients are used to determine scale dependent surface characteristics such as a power law (fractal) scaling of a surface. Finally, as we might expect, discrete wavelet transform coefficients are particularly useful for signal compression problems in engineering.

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